Turbo machine combustion assembly comprising an improved fuel supply circuit

ABSTRACT

Turbo machine combustion assembly ( 1 ) comprising a combustion chamber ( 10 ), at least one starting injector ( 17 ), a plurality of main injectors ( 18 ) distributed at constant angular intervals around the circumference of the combustion chamber, each starting injector being positioned between two consecutive main injectors, equal distances therefrom, and a fuel supply circuit ( 40 ) supplying fuel to the injectors, in which assembly the combustion chamber is delimited by two axisymmetric walls—an external wall ( 14 ) and an internal wall ( 12 )—which are connected by an annular chamber end wall ( 16 ), the fuel supply circuit being designed to supply at least one starting injector continuously, each continuously-supplied starting injector being oriented toward the chamber end wall and dimensioned to spread a spray (F) of fuel between 120° and 180° wide, and the flow rate of fuel injected by the main injectors ( 18′ ) between which the starting injectors are positioned being reduced by comparison with the flow rate injected by the other main injectors ( 18 ).

FIELD OF THE INVENTION

The invention relates to the field of turbomachines, and morespecifically the field of turbomachine combustion assemblies, comprisinga combustion chamber and a plurality of injectors dedicated to startingand supplying fuel to the combustion chamber.

PRIOR ART

With reference to FIG. 1, turbomachines 1 conventionally include acombustion chamber 10 and a distributor 20 housed in a casing 30, thecombustion chamber being delimited by axisymmetric outer 14 and inner 12walls extending one inside the other and which are connected by anannular chamber end wall 16.

The casing also has an inner wall 32 and an outer wall 31 to which theinner 12 and outer 14 walls of the combustion chamber are respectivelyfastened.

A mixture of air and fuel is injected into the combustion chamber by aplurality of injectors, this mixture being combusted to generate theenergy needed to propel the turbomachine.

Several types of injectors are positioned in a combustion chamber,including starting injectors 17, which form part of the ignition systemcomprising at least one spark plug. This ignition system makes itpossible to set the airfuel mixture alight, initiate combustion and makeit spread to the main injectors. The starting injectors generally enterthe combustion chamber through an opening formed in the outer wall ofthe combustion chamber.

To characterize the injectors a quantity known as Flow Number (FN) isused, equal to the flow rate of the injector in L/h divided by thesquare root of the pressure difference in bars of the injected mixturebetween its pressure at the input and the output of the injector.

The Flow Number of the starting injectors is less than the Flow Numberof the main injectors for a given turbomachine. The Flow Number of amain injector of a machine is typically of 3 to 10 times the Flow Numberof a starting injector of the same machine.

The Flow Number of a starting injector is typically between 1 and 4,preferably between 1.5 and 2, while that of a main injector is typicallygreater than 4, for example between 5 and 15, and advantageously between7 and 12.

This difference in Flow Number is the result of a difference in thefunctionality of the injectors: the initiation of the combustion in thechamber by the starting injectors requires a small quantity of fuel,while the continuation of combustion in the chamber by the maininjectors in order to give the turbomachine its power requires a muchhigher flow rate. Of course the FN values of the main injectors or thestarting injectors depend on the power and the thermodynamic cycle ofthe engine.

In socalled “rod” chambers, each main injector opens into apre-evaporation rod 19, which includes a duct equipped with two exhaustopenings opening into the combustion chamber.

During operation, the starting injectors initiate combustion by settingfire to the fuel using a spark plug, and thus heat the preevaporationrods.

The main injectors are then fueled to continue the combustion in thechamber by spraying fuel into the rod. During this step, the supply offuel to the starting injectors stops and they are drained to avoidcoking, which could cause them to clog up.

FIGS. 2 a and 2 b represent the fuel supply circuit enabling theimplementation of this combustion cycle, respectively in the phase ofignition of the chamber, when the starting injectors are supplied withfuel, and in the phase of drainage of said injectors.

The fuel supply circuit 40 comprises a supply duct for the startinginjectors 43, a fuel supply duct 44 for the main injectors 18, and afuel distribution duct 42, in fluid communication with the fuel supplyducts and suitable for supplying them with fuel.

This circuit further has a circuit 46 for draining the startinginjectors into the atmosphere, actuated by a starting electrovalve 47which, when it is actuated as in FIG. 2 b, shuts off fluid communicationbetween the distribution duct 42 and the supply duct 43 for the startinginjectors.

The fuel supply circuit 40 also comprises a level valve 45, suitable forshutting off fluid communication between the fuel supply duct of themain injectors 44 and the rest of the circuit when the pressure in thefuel duct, downstream of its connection with the fuel supply duct of thestarting injectors, is less than a predetermined threshold. This valve45 thus opens upon an increase in the pressure of the distributioncircuit following the increase in the flow rate of the fuel injectedinto the combustion chamber after the ignition has taken place toincrease motor speed.

Finally, the combustion chamber includes an antiextinction function inthe event of sudden reduction of the speed, to avoid having to reignitethe combustion chamber when the turbomachine is at its poststartingspeed.

This anti-extinction function is ensured by using a favored maininjector 180, which is the injector predominantly powered if the fuelpressure in the supply circuit is too low. To achieve this, adistribution valve 48 is provided between the supply circuit 49 of thefavored injector and the supply duct 44 of the other injectors to shutoff fluid communication with this duct in the event of a decrease in theflow rate.

The supply circuit is therefore a complex assembly with a highproduction cost due to the large number of parts it includes.

OVERVIEW OF THE INVENTION

The aim of the invention is to solve the abovementioned problem, byproposing a turbomachine combustion assembly comprising a simplifiedfuel supply circuit.

Regarding this, the invention proposes a turbomachine combustionassembly, comprising:

-   -   a combustion chamber,    -   at least one starting injector, suitable for initiating        combustion in the chamber,    -   a plurality of main injectors distributed at a constant annular        interval around the circumference of the combustion chamber,        designed to supply fuel to the combustion chamber when        combustion has been initiated, and    -   a fuel supply circuit for the injectors,        wherein the combustion chamber is delimited by two axisymmetric        outer and inner walls extending one inside the other and which        are connected by an annular chamber end wall, the combustion        assembly being characterized in that the fuel supply circuit is        designed to supply fuel to at least one starting injector        continuously, so that said injector is supplied with fuel both        throughout the initiation of the combustion and when fuel is        supplied to the chamber when the combustion has been initiated,        in that each continuously-supplied starting injector is oriented        toward the chamber end wall and is dimensioned to spread a spray        of fuel having an angular aperture in a first direction between        120° and 180°, and        in that the flow of fuel injected by the main injectors between        which the starting injectors are positioned is reduced by        comparison with the flow injected by the other main injectors,        and in that each starting injector is positioned between two        consecutive main injectors, at equal distance therefrom.

Advantageously, but optionally, the combustion assembly according to theinvention can further have at least one of the following features:

-   -   the supply circuit is designed to supply all the starting        injectors continuously.    -   The ratio of the flow rate divided by the square root of the        pressure difference of the fuel mixture between its pressure at        the input and at the output of the injector, for the main        injectors between which each starting injector is positioned, is        less than said ratio for the other main injectors.    -   Each continuously-supplied starting injector is dimensioned to        spread a spray having an angular aperture between 15 and 35° in        a second dimension orthogonal to the first direction.    -   The combustion chamber is of the chamber with aerodynamic or        aeromechanical injectors type.    -   The chamber is of the pre-evaporation rod type, each        pre-evaporation rod being shaped so that the fuel injected by        the main injectors is directed toward the chamber end wall.    -   The combustion chamber comprises:        -   on its inner wall, a plurality of air intake openings, and        -   on its outer wall, a plurality of socalled dilution            openings,            wherein the number and diameter of said openings are            designed to distribute the air intake in the combustion            chamber and to preserve the homogeneity of the temperature            field in said chamber.    -   The combustion chamber is a reverseflow chamber.    -   The fuel supply circuit comprises:        -   a supply duct for the starting injectors,        -   a supply duct for the main injectors, and        -   a fuel distribution duct, in fluid communication with the            supply ducts and designed to supply fuel to said ducts,            the supply circuit further comprising a distribution system            designed to shut off fluid communication between the fuel            distribution duct and the supply duct of the main injector            when the fuel pressure in the distribution duct is less than            a predetermined threshold.    -   The distribution system is further designed to distribute the        fuel flow between main injectors having a reduced flow rate and        the other main injectors.

Owing to the continuous supply of fuel to the starting injectors, thefuel supply circuit no longer needs to contain a drainage circuit.

In addition, the fact of continuously supplying fuel to the startinginjectors makes it possible to keep the chamber ignited even in theevent of a rapid decrease in the flow of fuel to the main injectors—forexample in the event of a reduction of the turbomachine speed. Thefavored injector function, and the adaptation of the fuel supply circuitprovided for this purpose are therefore removed.

Furthermore, the fact of adapting the spray of fuel spread by thestarting injectors and reducing the flow rate of the main injectorsadjacent to the starting injectors by comparison with that of the othermain injectors makes it possible to preserve the homogeneity of the fuelin the combustion chamber, and therefore maintain the lifetime of theparts downstream of the chamber.

DESCRIPTION OF THE FIGURES

Other features, aims and advantages of the invention will becomeapparent from the following description, which is purely illustrativeand nonlimiting, and must be read with reference to the appendeddrawings wherein:

FIG. 1, already described, represents an axial section view of aturbomachine of the prior art.

FIGS. 2 a and 2 b, also already described, represent a fuel supplycircuit for the injectors of a turbomachine of the prior art,respectively in a phase of supplying the starting injectors, and duringa phase of draining said injectors.

FIG. 3 a represents a partial section view of a turbomachine comprisinga combustion chamber of the preevaporation rod type,

FIG. 3 b represents a partial section view of a turbomachine comprisinga combustion chamber with aerodynamic or aeromechanical injectors.

FIG. 4 represents a fuel supply circuit for the injectors of aturbomachine.

FIG. 5 represents a crosssection view of a turbomachine,

FIG. 6 represents a partial perspective view of a combustion chamber ofa turbomachine,

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

With reference to FIGS. 3 a and 3 b, a turbomachine combustion assembly1 is represented, comprising a combustion chamber 10 and a casing 30(represented in FIG. 3 b), the combustion chamber 10 being delimited bytwo axisymmetric outer 14 and inner 12 walls extending one inside theother and which are connected by an annular chamber end wall 16.

The casing also comprises an outer wall 31 (represented in FIG. 3 b) andan inner wall (not represented in FIG. 3 b) to which the inner 12 andouter 14 walls of the combustion chamber are respectively fastened.

The turbomachine 1 further comprises a plurality of fuel injectors,comprising at least one starting injector 17, preferably at least twostarting injectors 17, and a plurality of main injectors 18, preferablyat least three main injectors 18, for example eight main injectors.

The ignition system comprises at least one starting injector 17 and twospark plugs (not represented) suitable for setting the spray of fueldelivered by the injector 17 alight and thus initiating combustion inthe chamber.

According to a first embodiment of the turbomachine, represented in FIG.3 a, the combustion chamber is of the preevaporation rod type, whereineach main injector 18 opens into a preevaporation rod 19, itself openinginside the chamber. Each pre-evaporation rod comprises a duct openingvia two openings into the combustion chamber.

The pre-evaporation rods 19 enter the combustion chamber through anopening formed in the outer wall 14 or in the chamber end wall 16 of thecombustion chamber 10, and having a Tshaped section, the ends of whichare curved toward the chamber end wall.

According to a second embodiment of the turbomachine, represented inFIG. 3 b, the main injectors 18 are of aerodynamic or aeromechanicaltype, and directly enter the chamber 10 through an opening formed in thechamber end wall 16.

Advantageously, the combustion chamber is of reverse flow type.

The turbomachine 1 also comprises a fuel supply circuit 40 for theinjectors, said circuit being represented in FIG. 4.

The fuel supply circuit comprises a fuel injection inlet 41, by whichthe fuel enters the circuit along a fuel distribution duct 42.

The fuel distribution duct is connected to the starting injectors by asupply duct 43 for the starting injectors, and to the main injectors bya supply duct 44 for the main injectors.

The fuel supply circuit is designed to supply fuel to the startinginjectors continuously, so that said injectors are supplied with fuelboth during a step of initiating the combustion in which the fuel is setalight by the spark plug, and during the later step of supplying fuel tothe chamber, when the combustion has already been initiated.

To proceed with the continuous supply of fuel to the starting injectors,the circuit comprises a distribution system 45 designed to shut offfluid communication between the fuel distribution duct and the supplyduct for the main injectors, for example when the pressure of the fuelin the distribution duct is less than a predetermined threshold.

The fuel is thus directed in a way that favors the starting injectors,and it is only upon an increase in fuel pressure—for example followingan increase in the speed of the turbomachine—that the main injectors aresupplied.

Because the starting injectors are continuously supplied, it is notnecessary to drain them. The drainage circuit is therefore removed andthe fuel supply circuit is simplified.

Furthermore, the favored injector function is also removed due to thefact that the starting injectors perform this function by beingpermanently supplied with fuel: in the event of a drop in the speed ofthe turbomachine, the starting injectors remain supplied with fuel andtake over the anti-extinction function by continuing combustion insidethe chamber.

Due to this, the distribution valve of the injectors, which makes itpossible to favor one main injector, is removed, and the fuel supplycircuit is further simplified and made less expensive to manufacture.

The structure of the combustion chamber and the position of theinjectors must be suitable for preserving a good homogeneity of thetemperature fields inside the chamber and at the chamber output.

To do this, returning to FIG. 3 a, if the combustion chamber is of thepre-evaporation rod type, the starting injectors 17 and the outletopenings of the pre-evaporation rods 19 are oriented toward the chamberend wall 16.

Alternatively, in the case of a combustion chamber with aerodynamic oraeromechanical injectors, as illustrated in FIG. 3 b, the startinginjectors 17 are oriented toward the chamber end wall.

In this way, the fuel is directly injected into the moving stream ofcombusting fuel, known as “recirculation”.

This increases the time that the fuel outputted by the starting injector17 can spend in the primary area of the combustion chamber, i.e. thearea wherein evaporation and combustion take place. The combustion ofthe fuel in the primary area is thus almost total, which allows the fuelinjected by the starting injectors to behave in a similar way to thefuel injected by the preevaporation rods, so that the continuous use ofsaid injectors has no negative effect on the overall combustionefficiency or the pollutant emissions.

In addition, starting injectors of “Flat Spray” type are used. i.e. ofthe type in which the crosssection of the spray F (see FIG. 5) has alarge angular aperture in a first direction, between 120° and 180°, anda reduced angular aperture in a second direction, orthogonal to thefirst, between 15 and 35°.

The spray of the starting injectors is oriented against the chamber endwall so that the second direction, corresponding to the reduced angularaperture, is radial about the axis of the turbomachine, as illustratedin FIG. 5.

The use of Flat Spray starting injectors makes it possible to spread theregular contribution of fuel over a wider angular sector and thus toobtain a homogenous temperature field in the primary area of thecombustion chamber.

In addition, with reference to FIG. 5, the main injectors 18 areregularly distributed around the circumference of the combustionchamber, i.e. with a constant angular interval between two consecutivemain injectors.

The starting injectors are positioned between two consecutive maininjectors and at equal distance therefrom, so that the openings of thepre-evaporation rods 19 into which the main injectors open arepositioned facing the ends of the spray of the starting injectors.

In order to avoid a local over-richness of fuel in the combustion areain the vicinity of the starting injectors, i.e. a surplus of local flowgenerated by the constantly supplied starting injectors, the maininjectors 18′ between which the starting injectors are positioned have aflow rate that is reduced by comparison with the flow rate of the othermain injectors 18.

This reduction in flow rate can be obtained by reducing the Flow Numberof the injectors 18′ by comparison with that of the injectors 18.Specifically, this has the advantage of supplying the main injectors 18and 18′ with the same injection pressure, which makes it possible tosimplify the fuel circuit upstream of the injectors.

By way of non-limiting example, the set of main injectors has a FlowNumber greater than 4, for example between 5 and 15, advantageouslybetween 7 and 12, but advantageously, the reduced Flow Number of theinjectors 18′ is between 6 and 8, preferably equal to 7, and the FlowNumber of the other main injectors is greater than or equal to 9. TheFlow Number of the starting injectors, meanwhile, is between 1 and 4,preferably between 1.5 and 2.

Of course, the Flow Number of the injectors depends on variableparameters such as the size of the turbomachine, the number ofinjectors, or else the maximum fuel flow rate. Those skilled in the artwill be able to adjust the value of the Flow Number of the variousinjectors used according to the turbomachine on which these injectorshave been fitted.

Finally, for high-power speeds, the Flow Number values must be adjustedto minimize the difference in fuel flow rate between a chamber sectorcorresponding to a preevaporation rod and a sector corresponding to apreevaporation rod and a starting injector.

For example, if the turbomachine comprises eight main injectors, four ofthem can have a reduced Flow Number.

Returning to FIG. 5, if the flow rate of the injectors 18′ is reduced bycomparison with that of the other main injectors 18, without the FlowNumber being reduced, the distribution system 45 is also designed todistribute the fuel flow between the various types of injectors (i.e.distribute a lower flow to the injectors 18′). In this respect it canfurther comprise a supply duct 44′ for the injectors 18′, advantageouslyindependent of the supply duct 44 for the injectors 18 to allow the fuelsupplied to said injectors 18′ to be at a different pressure from thatsupplied to the injectors 18.

With reference to FIG. 6, a combustion chamber is represented in partialperspective view. The chamber includes a primary area, extending fromthe chamber end wall to an axial position corresponding to the axialposition of the air intake openings 13 positioned on the inner wall 12of the combustion chamber 10 known as “primary holes”, the axialposition being measured parallel to the axis of the turbomachine. Thisaxial position is for example positioned at about 40 mm from the chamberend wall.

The air intake openings 15 are distributed around the circumference ofthe combustion chamber so that, for each pre-evaporation rod 19, two airintake openings are facing one opening of the rod, and one air intakeopening is facing the other opening of the rod.

A socalled dilution area extends from the primary area to an axialposition corresponding to the axial position of dilution openings 15positioned on the outer wall 14 of the chamber, this axial positionbeing at approximately 70 mm from the chamber end 16.

The number and diameter of the dilution openings and/or that of theintake openings can be adapted in order to angularly adapt the rate ofair intake into the chamber. This makes it possible to control thetemperature field in the combustion chamber, for example to remove anyhot spots generated by the instantaneous increase in fuel richness dueto the continuous supply of fuel to the starting injectors. Thisadaptation makes it possible to preserve the lifetime of the parts ofthe turbomachine, particularly downstream of the combustion chamber.

For example, the dilution openings and intake openings can have adiameter between 4 and 7 mm, preferably between 5 and 6 mm. This makesit possible to remove any hot spots in the combustion chamber, whichpreserves the lifetime of the turbomachine parts. Of course, the numberand size of the primary openings and the dilution openings depend onvariable parameters such as the size of the turbomachine, the number ofinjectors or else the flow rate of air into the engine. Those skilled inthe art will be able to adjust the number and size of the openingsaccording to the turbomachine on which the combustion chamber has beenfitted.

Thus, a turbomachine is proposed, the fuel supply circuit of which issimplified due to the continuous supply to the starting injectors,without impairing the lifetime of the parts of the turbomachine.

1. A turbomachine combustion assembly, comprising: a combustion chamber,at least one starting injector, suitable for initiating combustion inthe chamber, a plurality of main injectors distributed at a constantannular interval around the circumference of the combustion chamber,designed to supply fuel to the combustion chamber when combustion hasbeen initiated, and a fuel supply circuit for the injectors, wherein thecombustion chamber is delimited by two axisymmetric outer and innerwalls extending one inside the other and which are connected by anannular chamber end wall, the combustion assembly being characterized inthat the fuel supply circuit is designed to supply fuel to at least onestarting injector continuously, so that said injector is supplied withfuel both throughout the initiation of the combustion and when fuel issupplied to the chamber when the combustion has been initiated, in thateach continuously-supplied starting injector is oriented toward thechamber end wall and is dimensioned to spread a spray (F) of fuel havingan angular aperture in a first direction between 120° and 180°, and inthat the flow of fuel injected by the main injectors between which thestarting injectors are positioned is reduced by comparison with the flowinjected by the other main injectors, and in that each starting injectoris positioned between two consecutive main injectors at equal distancetherefrom.
 2. The turbomachine combustion assembly according to claim 1,wherein the supply circuit is designed to supply all the startinginjectors continuously.
 3. The turbomachine combustion assemblyaccording claim 1, wherein the ratio of the flow rate divided by thesquare root of the pressure difference of the fuel mixture between itspressure at the input and at the output of the injector for the maininjectors between which each starting injector is positioned is lessthan said ratio for the other main injectors.
 4. The turbomachinecombustion assembly according to claim 1, wherein eachcontinuously-supplied starting injector is dimensioned to spread a spray(F) having an angular aperture between 15 and 35° in a second dimensionorthogonal to the first direction.
 5. The combustion assembly accordingto claim 1, wherein the combustion chamber is of the type havingaerodynamic or aeromechanical injectors.
 6. The combustion assemblyaccording claim 1, wherein the chamber is of type comprisingpre-evaporation rods, each pre-evaporation rod being shaped so that thefuel injected by the main injectors is directed toward the chamber endwall.
 7. The turbomachine combustion assembly according to claim 6,wherein the combustion chamber comprises: on its inner wall, a pluralityof air intake openings, and on its outer wall, a plurality of so-calleddilution openings, wherein the number and diameter of said openings aredesigned to distribute the air intake in the combustion chamber and topreserve the homogeneity of the temperature field in said chamber. 8.The turbomachine combustion assembly according to claim 7, wherein thecombustion chamber is a reverse-flow chamber.
 9. The turbomachinecombustion assembly according to claim 8, wherein the fuel supplycircuit comprises: a supply duct for the starting injectors, a supplyduct for the main injectors, and a fuel distribution duct, in fluidcommunication with the supply ducts and designed to supply fuel to saidducts, the supply circuit further comprising a distribution systemdesigned to shut off fluid communication between the fuel distributionduct and the supply duct for the main injectors when the fuel pressurein the distribution duct is less than a predetermined threshold.
 10. Thecombustion assembly according to claim 9, wherein the distributionsystem is further designed to distribute the fuel flow between maininjectors having a reduced flow rate and the other main injectors.
 11. Aturbomachine comprising a combustion assembly according to claim 10.